Airborne irritants can be distributed in the home or workplace. These irritants can include, among other things, molds, pollen, bacteria, dust, and viruses. The spread of these particles can produce serious reactions among those who are sensitive. Even among those who are less-sensitive, longterm exposure to contaminated air may cause respiratory or other health problems. Breathing cleaner air generally leads to improved health.
In recognition of the relationship between clean air and improved health, several types of air purifiers have been developed. U.S. Pat. No. 5,435,817 issued to Davis et al., discloses a portable room air purifier that uses a HEPA filter to remove airborne irritants. The Davis device includes spiraled discharge scrolls that distribute air uniformly around the device. The Davis device does not kill pathogens collected on the HEPA filter element; micro-organisms can continue to grow once trapped. Furthermore, extremely-small organisms, like viruses, may pass directly through a HEPA filter element.
Other devices use ultraviolet (UV) light to kill pathogens. In some instances, UV lamps are placed directly within the ductwork of central air conditioning units. These devices are designed to expose air passing through the duct to shortwave UV light, typically 254 nm. This wavelength is destructive to the DNA of many micro-organisms. As a result, shortwave UV light has germicidal effects. Repeated or prolonged exposure to this type of UV light can significantly reduce live bacteria, mold spores, and virus levels in treated air. Unfortunately, while duct-mounted UV lamps may improve the air quality in some buildings, these devices require specialized installation. Also, the units may not be readily transferred from one building to another.
Some portable air purifiers, like that disclosed by U.S. Pat. No. 4,017,736 have been designed to incorporate shortwave UV light. Unfortunately, exposure to shortwave UV light can produce negative side effects. The human eye is particularly sensitive to shortwave UV light. Exposure to shortwave UV light may, for example, cause an inflammatory eye condition known as photokeratitis, which may cause pain and sensitivity to light. Louvered openings, perforated screens, and filter elements are not effective in visually blocking light from an ultraviolet light source.
A portable device that includes a shortwave UV light source must also include safety features that reduce the likelihood of unwanted exposure to UV light. Some UV-including air purifiers rely on shutoff switches to disable UV lamps if the device is opened. Although shutoff switches prevent direct UV exposure when a device is open, they do not reduce exposure to ambient UV light that may leak through inlet or outlet ports while the device is operating. Other UV-including devices cover inlet or outlet ports with mesh screens to reduce ambient UV light exposure. Although filter screens may reduce exposure to ambient UV light, prolonged exposure to the area around these screens is still not recommended. These screens also reduce airflow efficiency. Additionally, these screens are only effective when installed correctly. A screen that has been removed for cleaning may not be reseated properly. In other situations, inlet and outlet screens may be removed in an attempt to increase airflow through the device. Operating a UV-including purifier with ill-fitting, or missing, filter screens may produce unacceptable levels of exposure to shortwave UV light. Ironically, many UV-including devices may eliminate one type of problem only to create others.
Thus, what is needed is a portable room air purifier that includes advantages of the known devices, while addressing the shortcomings they exhibit. The air purifier should include a High Efficiency Particulate Air (HEPA) filter and a germicidal shortwave UV light source. The air purifier should also include safety features that allow safe usage of the device in all environments, including those in which curious children present. The air purifier should also include features that promote free airflow, regardless of the location of the purifier within a given room. The purifier should be compact and easily transported from one room to another, as needed. The device should also be lightweight enough to be placed on a variety of supporting surfaces.